Hello Hanuman, Please see the answer.
Since you are growing Ge on Si(100), so first of all you should align your XRD systems to search for Si(100) peaks and maximize the substrate signal's intensity upto the limit defined by the detector.
So once you do a theta-2theta scan, then u should see some peaks that are due to Ge(100). You can index those to the Ge diffraction pattern. If u just see Ge (100) peaks, then you have the possibility of epitaxy. If you film is thin enough, smooth enough, then you might see pendellosung fringes also.
You need to do rocking curves for the Ge film peak, then if the full width half maximum (FWHM) is narrow the quality of the film is good.
You also need to do theta-2theta along an off axis direction for example Si(112) and then do rocking for the off-axis peak to get the crystalline quality. Finally, you need to do a phi scan for the film and substrates off-axis peaks and compare them so that find out what is the epitaxial relations between these two.
Another thing to do is a GIXRD (grazing incidence x-ray diffraction ) scan, if there are any polycrystalline regions, then they will show up the GIXRD measurements, if there are no poly region, then you should not see any signal in the GIXRD peaks(just a decay due to the lorentzian background), possible exception being some substrate peaks that are present because of way the diffractometer is aligned.
All these measurements whould help you in checking if your films are epitaxial or not.
Hope this helps
Paritosh
Hi,
Since the Ge was deposited by MBE it would be epitaxial on Si. Do rocking curve for a (004) or (002) reflection (symmetric reflection) as Paritosh mentioned you should optimize the Si (004) peak intensity first. You did not mention the thickness of Ge film if the thickness is less than the critical thickness the Ge film will be strained, in-plane compresssion and out-of-plane elongation. So for (004) reflection, the separation between the two peaks would give the out-of-plane strain. If the thickness is beyond critical thickness the strain would have relaxed and then you'll have to do asymmetric reflection such as (224) or (115) to get information about strain relaxation.
Hi Hanuman,
If you are depositing 250 nm of Ge on Si, then you are certainly above the critical thickness for either plastic or elastic relaxation, probably even both. This will have severe influence on your XRD signal. Checking the surface of your sample by e.g. AFM before the XRD measurements will be certainly helpful for you.
Hi,
True that's a thick film beyond equilibrium critical layer thickness of Ge on Si. So it may be a completely strain relaxed film, you can see slightly broad Ge layer peak in XRD (004) or (002) scan. There are several other related issues, depending on your buffer layer growth before depositing Ge on Si. Subsequent analysis depends on what exactly you want from XRD. May be try other characterization techniques such as TEM to visualize the misfit dislocations and may be AFM as suggested by Moritz to understand effects of strain relaxation on the surface.....etc.
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